1. Field of the Invention
This invention relates to a method for adjusting the profile of a conductor roll. More particularly, it relates to a method for adjusting the profile of the outer surface of a conductor roll used in a radial plating apparatus for electroplating zinc or another metal onto one surface of a steel strip.
2. Discussion of the Prior Art
A typical radial plating apparatus is disclosed in U.S. Pat. Nos. 3,483,113 and 3,634,223. Apparatus of the type disclosed in these patents is schematically shown in FIG. 2. The apparatus includes a tank 1 containing electrolyte or plating solution 2, a conductor roll 3 partially immersed in the plating solution 2, and upstream and downstream deflector rolls 4, 4 disposed above opposed sides of the tank. A steel strip 5 is passed around upstream roll 4, conductor roll 3 and downstream roll 4 so that the strip 5 moves through the plating solution. The apparatus further includes a soluble anode 7 held by a main anode 6, both immersed in the solution, and optionally a roll polisher 8 in contact with the conductor roll 3 for removing a foreign matter. During movement of the strip 5 along the conductor roll 3, conduction of electricity causes plating metal to be dissolved out from the soluble anode 7 to deposit on the outside surface of the strip 5. In the case of an insoluble anode, metal ions in the solution are deposited.
The structure of the conductor roll 3 is shown in FIG. 3. The roll 3 includes a hollow metal cylinder 10, a conductor ring 11 at an intermediate of the outer circumference of the cylinder 10, and rubber linings 12 disposed on the cylinder 10 at the opposite sides of the ring 11. The interior of the roll 3 is cooled with coolant in the form of cooling water for absorbing the Joule heat created by plating current as shown by an arrow 13 indicating the flow of coolant.
As the strip 5 moves with the conductor roll 3 of this structure, the rubber linings 12 seal the opposite edges of the strip to prevent plating on the inside surface thereof. The rubber linings 12 are thus required to be corrosion resistant against the plating solution 2, fully stretchable to achieve a sealing function, and hard enough to be wear resistant.
However, it is difficult to obtain a material which meet all these requirements. Generally, a rigid rubber with Hs of about 90 having corrosion and wear resistance is used. Since this rubber allows only a relatively small amount of contraction and sretch, the surface level of the rubber lining 12 must be the same as or lower than that of the conductor ring 11 in order to maintain an intimate contact between the conductor ring 11 and the strip 5. Usually the surface level of the rubber lining 12 is lower than that of the conductor ring 11, as viewed in a radial direction, to form a step S therebetween as shown in FIG. 3. The components are usually designed and polished such that the distance of the step S falls in the range of from 0.1 to 0.3 mm.
The conductor ring 11 and the rubber lining 12 wear away due to contact with the strip 5 during operation. Since the rubber lining is more worn than the metal ring, the surface profile of the conductor roll 3, that is, the step S between the surfaces of the conductor ring 11 and the rubber lining 12 changes during operation. The conductor ring 11 can be more worn out when the roll polisher 8 is located in contact with the conductor ring 11.
The roll profile or the step S between the surfaces of the conductor ring 11 and the rubber lining 12 largely affects the quality of plating on the strip 5. If the step S becomes as large as 0.5 mm or more, the strip 5 is bent at the site of the step S as shown at A in FIG. 4a. If the conductor ring 11 is more worn than the rubber lining 12 to give a negative step as shown at B in FIG. 4b, the strip 5 cannot be held in full contact with the conductor ring 11, causing plating irregularities. It is thus very important to maintain a proper roll profile. In the prior art, the roll must be resurfaced once a year in order to maintain the step S in the range of from 0 to 0.5 mm. Replacement of the roll lowers productivity and the polishing operation is expensive.